In the construction and assembly of instrument movements having indicator hands, such as thermometers, barometers, wind speed indicators, etc., it is highly desirable to be able to quickly and positively place an indicator hand in operative association with the instrument movement. It is also highly desirable to do this is in an inexpensive manner. However, many conventional commercial techniques, such as the utilization of a threaded brass arbor and internally threaded brass cap nut, are both expensive and time consuming to assemble.
According to the present invention, a cap nut for an instrument having an indicator hand, as well as a subassembly for such an instrument, and related assembly, allow not only quick assembly of an indicator hand to the instrument, but do so in an inexpensive manner. By practicing the invention the assembly time may be reduced by about 15 to 20 seconds compared to an assembly with conventional brass threaded arbors and cap nuts, and the cost can be reduced to only a fraction of the cost of such an arbor and cap nut.
According to one aspect of the present invention an assembly for an instrument having an indicator hand is provided. The assembly comprises the following elements: A plastic arbor. A plastic cap nut. An indicator hand adapted to be held in a predetermined position by the arbor and the cap nut. And, non-threaded engagement means of the arbor and the cap nut for holding the arbor and cap nut together, to in turn hold the indicator hand in place. The cap nut may be an integral body of plastic such as styrene, with a substantially continuous surface at a first side, and a recess in the second side, with an elongated projection extending out from the recess. The arbor also may be of high impact styrene, and have an elongated axially extending opening at one end and slotted at the other end. The cap projection is preferably smooth surfaced and circular in cross-section, having a maximum diameter of about one-fifth to one-sixth of the diameter of the integral body of plastic.
According to another aspect of the present invention a subassembly for an instrument is provided. The subassembly comprises the following components: An indicator hand having means defining an opening therein. An arbor having a first portion thereof which is dimensioned and shaped to fit through the opening. A cap nut. And, interference fit surface manifestations formed on the arbor and the cap nut to allow the cap nut and arbor to be quickly assembled, and to hold the indicator hand in a predetermined position with respect to the arbor and cap nut when the arbor passes through the opening in the indicator hand.
Still further the invention contemplates a cap nut per se. The cap nut comprises: An integral body of plastic. Means defining a substantially continuous surface at a first side of the body. Means defining a recess at a second side of the body, opposite the first side. And, an elongated projection extending out from the recess along a central axis of the body substantially concentric with the recess and the substantially continuous surface.
It is the primary object of the present invention to provide an easy to assemble press-on cap nut and arbor assembly that it is also inexpensive. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.